This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-187874, filed Jun. 22, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an X-ray CT (computed tomography) apparatus, particularly, to a mechanism for detecting the rotation of a rotary section of a gantry included in the X-ray CT (computed tomography) apparatus and to the control of the detecting mechanism.
In recent years, the function of the X-ray CT apparatus has been enhanced and diversified. One of the diversifications of the function is small sound imaging, i.e., the situation in which mechanical vibration is suppressed as much as possible so as to photograph a patient to be examined in a quiet operating environment. In a system in which the rotary driving force generated from a motor arranged in the stationary section of the gantry is transmitted via a gear, a belt, etc. so as to drive the rotary section, a big operating sound (noise) is generated by, for example, the sliding of the belt so as to produce anxiety or unpleasantness in the patient or the X-ray engineer. In these circumstances, the sound suppressing technology is applied to the rotary driving mechanism of the X-ray CT apparatus in order to prevent such a noise.
One of the technologies that has appeared in accordance with the trend toward small sound imaging is an X-ray CT apparatus in which a direct drive (DD) motor driving system is applied to the rotary mechanism of the gantry. In the direct drive motor driving system, a large number of magnets are mounted to the rotary section of the gantry. At the same time, a winding is mounted to the stationary section of the gantry. By supplying an electric current to the winding, the rotary section of the gantry is directly rotated as a rotor of the motor. The mechanism for transmitting the rotating force such as a belt and a gear is not included in the direct drive motor driving system, making it possible to suppress the sound.
A resolver mechanism is mounted to the X-ray CT apparatus employing such a direct drive motor driving system in order to detect the rotation of the rotary section of the gantry and to control the rotating position and the rotation speed.
FIG. 1 schematically shows the conventional resolver mechanism. As shown in FIG. 1, a resolver 300, a transformer 301, and a direct drive (DD) motor 302 are mounted to the gantry rotary section and the gantry stationary section included in the X-ray CT apparatus. These members are mounted to the structure on the side of the gantry rotary section and to the structure on the side of the gantry stationary section. For example, the primary winding of the transformer 301 and the secondary winding corresponding to the resolver are mounted to the gantry rotary section and the gantry stationary section.
The resolver 300 applied to the X-ray CT apparatus, which is used for detecting the rotating position of the gantry rotary section and for detecting the rotating speed or rate, is shaped like a ring having a relatively large diameter and conforming with the shape of the gantry rotary section. A reference signal consisting of a Sin wave is generated from a reference signal generator 305 for the resolver, which is mounted in the rotary section of the gantry, so as to be supplied to the resolver 300. Upon receipt of the reference signal, the resolver 300 generates a sin signal and cos signal, and these signals are supplied to a controller 306 mounted in the stationary section of the gantry. These sin signal, cos signal and the reference signal generated from the reference signal generator 305 through the transformer 301 are converted into a digital signal by an R/D circuit (reference/detection signal processing circuit) so as to form the basic pulse. The frequency of the digital signal is divided so as to be utilized for detecting the position of the rotary section. To be more specific, the basic pulse is supplied to the control section of the X-ray CT apparatus so as to be utilized for various control operations based on, for example, the detection of the rotary position and the detection of the rotating speed, thereby controlling the explosion of the X-ray, the data collection and the trigger of an X-ray tube.
The rotary detection mechanism utilizing the resolver described above gives rise to problems as described below.
First of all, the resolver is a structure having a large diameter. For the mass production of the resolver, large scale automation facilities are required, leading to a high manufacturing cost of the X-ray CT apparatus. Also, in the conventional gantry rotary section having the resolver mechanism incorporated therein, a large resolver structure, etc. is arranged behind a data transfer unit for transmitting data by optical communication utilizing an LED or a photo diode between the gantry stationary section and the rotary section. As a result, it is difficult to gain access to the resolver mechanism in performing, for example, a maintenance operation, giving rise to the problem that much labor is required for the inspection, the renewal operation, etc. It should also be noted that a signal transmitting line is drawn directly from the coil of the resolver mechanism in order to take out signals from the coil of the resolver mechanism. What should be noted is that, in the event of, for example, wire breakage, it is difficult to cope with the wire breakage problem flexibly, with the result that it is unavoidable to renew the entire resolver.
An additional problem to be noted is that the resolver is incapable of executing the function of detecting the rotation unless the reference signal generator for generating the reference signal is mounted to the stationary section of the gantry as described above so as to supply power to the entire rotary section and stationary section of the gantry via a slip ring. This particular construction is undesirable in terms of efficiency and safety in the maintenance step. Under these circumstances, vigorous efforts are being made in an attempt to develop a new improvement capable of overcoming the problems inherent in the mechanism for detecting the rotation by a resolver.
An object of the present invention is to provide an X-ray CT apparatus simple in construction, permitting the maintenance operation at a low cost, and capable of detecting rotation and controlling the rotation with a high accuracy.
According to a first aspect of the present invention, there is provided an X-ray CT apparatus, comprising:
a gantry including a substantially cylindrical rotary section and a stationary section rotatably holding the rotary section;
rotation detecting means for detecting the rotation of the rotary section to generate a rotation detecting signal;
correcting means for correcting the rotation detecting signal; and
calculating means for calculating at least one of the rotating position and the rotating speed of the rotary section on the basis of the corrected detecting signal from the correcting means.
According to a second aspect of the present invention, there is provided an X-ray CT apparatus, comprising:
a gantry including a substantially cylindrical rotary section and a stationary section rotatably holding the rotary section;
rotation detecting means for detecting the rotation of the rotary section to generate a rotation detecting signal, the rotation detecting means including a target section to be detected, which is mounted to one of the rotary section and the stationary section to impart a periodic change in the magnetic flux in the rotating direction of the rotary section, and a rotation detecting sensor mounted to the other of the rotary section and the stationary section with a gap provided between the target section to detect the change in the magnetic flux generated in the target section in accordance with rotation of the rotary section and to generate a rotation detecting signal in accordance with detection of the change in the magnetic flux;
a sensor for detecting a reference position of the rotary section to generate a reference position detecting signal;
calculating means for calculating at least one of the rotating position and the rotating speed of the rotary section on the basis of the detection signal, the calculating means calculating the rotating position of the rotary section on the basis of the reference position signal generated from a position sensor and the rotating speed of the rotary section and also calculating a correction amount conforming with the position from the rotation detecting signal; and
moving means for slightly moving the rotation detecting sensor relative to the target section in accordance with the correcting amount to maintain constant the gap between the target section and the rotation detecting sensor.
Further, according to a third aspect of the present invention, there is provided an X-ray CT apparatus, comprising:
a gantry including a substantially cylindrical rotary section and a stationary section rotatably holding the rotary section;
rotation detecting means for detecting the rotation of the rotary section to generate a rotation detecting signal, the rotation detecting means including a ring-like target section to be detected, which is mounted to any one of the rotary section and the stationary section and having a periodic slit pattern formed therein, and an optical sensor mounted to the other of the rotary section and the stationary section in a manner to face the target section to detect the light ray passing through the slit pattern of the target section in accordance with rotation of the rotary section and, thus, to generate a detection signal;
correcting means for correcting the rotation detecting signal; and
calculating means for calculating at least one of the rotating position and the rotating speed of the rotary section on the basis of a corrected detecting signal from the correcting means.
Yet further, according to a fourth aspect of the present invention, there is provided an X-ray CT apparatus, comprising:
a gantry including a substantially cylindrical rotary section and a stationary section rotatably holding the rotary section;
detectable section, mounted on one of the rotary section and the stationary section, for applying a periodical change on a magnetic flux generated in a circumferential space which is coaxially defined around the rotary section;
detecting means, mounted on the another of the rotary section and the stationary section, for detecting the change of the magnetic flux which is produced due to the rotation of the rotary section, to generate a rotation detecting signal; and
calculating means for calculating at least one of the rotating position and the rotating speed of the rotary section on the basis of the detecting signal from the detecting means.
Furthermore, according to a fourth aspect of the present invention, there is provided an X-ray CT apparatus, comprising:
a gantry including a substantially cylindrical rotary section and a stationary section rotatably holding the rotary section;
motor for directly driving the rotary section to rotate the rotary section;
ring-shaped detectable section mounted on one of the rotary section and the stationary section and having a plurality of slits periodically arranged on the section;
detecting means, mounted on the another of the rotary section and the stationary section, for detecting light rays passing through the slit to generate a rotation detecting signal; and
means for generating an encoded signal based on the rotation detection signal from the detecting means.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.